After focusing on an object with the low power objective lens, you are trying to bring it into focus under the 40x objective lens, but the field of view is very dark. Which of the following may remedy this problem?

Choice A rationale: The cell membrane did not change at all because of the protection of the cell wall is incorrect because the cell wall does not prevent the movement of water across the cell membrane. The cell wall only provides mechanical support and prevents the cell from bursting in a hypotonic solution.

Choice B rationale: The cells burst because the solution was hypotonic is incorrect because the solution was hypertonic, not hypotonic. A hypertonic solution has a lower concentration of water than the cell, so water moves out of the cell and into the solution by osmosis, causing the cell to shrink.

Choice C rationale: The cell membrane shrank, but the central vacuole remained full is incorrect because the central vacuole also loses water in a hypertonic solution. The central vacuole is a large organelle that stores water and other substances in the plant cell. When water leaves the cell, the central vacuole shrinks and the cell loses its turgor pressure.

Choice D rationale: The cell membrane shrank away from the cell wall because the solution was hypertonic is correct because this is what happens when a plant cell is placed in a hypertonic solution. The cell membrane and the cytoplasm contract and pull away from the cell wall, creating a gap between them. This is called plasmolysis and it can damage the cell.

Choice E rationale: The cell became turgid is incorrect because the cell becomes turgid in a hypotonic solution, not a hypertonic one. A hypotonic solution has a higher concentration of water than the cell, so water moves into the cell and out of the solution by osmosis, causing the cell to swell and press against the cell wall. This is called turgor and it helps the cell maintain its shape and rigidity.

Choice A rationale: Transfer pipette is correct because you need a transfer pipette to transfer a drop of water or a liquid specimen onto the center of the slide. A transfer pipette is a plastic or glass tube with a bulb at one end that can suck up and release liquids.

Choice B rationale: Clean slide is correct because you need a clean slide to place the specimen on. A slide is a thin, flat piece of glass or plastic that can be viewed under a microscope. A clean slide ensures that there is no contamination or interference from other substances.

Choice C rationale: Bunsen burner is incorrect because you do not need a Bunsen burner to make a wet mount. A Bunsen burner is a device that produces a flame by mixing gas and air. A Bunsen burner is used for heating, sterilizing, or burning substances, not for making a wet mount.

Choice D rationale: Timer is incorrect because you do not need a timer to make a wet mount. A timer is a device that measures or indicates the passage of time. A timer is used for timing experiments, not for making a wet mount.

Choice E rationale: Tweezers is correct because you need tweezers to pick up and place the specimen on the slide. Tweezers are a pair of metal or plastic pincers that can grasp and hold small objects. Tweezers are useful for handling delicate or microscopic specimens.

Choice F rationale: Cover slip is correct because you need a cover slip to cover the specimen on the slide. A cover slip is a thin, transparent piece of glass or plastic that can be placed over the specimen on the slide. A cover slip protects the specimen from drying out, dust, or damage, and creates a flat surface for viewing under the microscope.